Organic light emitting devices (OLEDs) make use of organic thin film materials which emit light when excited by electric current. These devices usually consist of a sandwich structure with organic thin films deposited onto a transparent substrate and covered by top metal cathode contacts. Between the transparent substrate and the organic thin films is a layer of transparent, conducting material which serves as an anode.
The organic thin films typically consist of an emission layer between a hole transporting layer and an electron transporting layer. When current is applied between the cathode and anode, the emission layer provides a recombination site for electrons injected from the electron transporting layer and holes from the hole transporting layer. This recombination results in the emission of light having a characteristic wavelength depending on the organic materials used. Alternatively, single-layer organic or organic blend layers can be used instead of such multilayer organic thin film systems.
Because of its transparency, high conductivity and efficiency as a hole injector into organic materials, indium-tin-oxide ("ITO") is widely used as the anode material in OLEDS. Because the organic thin films are in direct contact with the ITO in OLEDs, the surface properties of ITO are expected to directly affect the characteristics of these devices. Consequently, ITO layers which are not properly cleaned or have other imperfections can result in poor device performance, such as shorting, unstable I-V characteristics, higher drive voltages and poor reliability.
To minimize the possibility of poor device performance due to the ITO layer, conventional ITO treatments usually include combinations of cleaning steps, such as sonification, boiling and rinsing in materials such as detergents, deionized ("DI") water and organic solvents, and degreasing in organic solvent vapor. Such cleaning techniques, however, are not often sufficiently reliable or reproducible, and consequently, irregular variations in device performance often occurs.